In this project, amorphous calcium phosphate (ACP), an important intermediate in the formation of apatite, is being investigated for possible use as a dental material. When either used alone, or in combination with other dental materials, especially polymeric resins, ACP has a wide range of possible applications such as in restorative composites, cavity liners and bases, luting and pulp capping agents, prophylactic and endodontic sealants, and as a component in periodontic packs and impression pastes. The hypothesis is that as a component in appropriate resin-based composites, sealants and adhesives, ACP may be useful as a remineralization agent. In this regard, ACP-embedded, methacrylate resins, which release calcium and phosphate ions at levels that exceed the thermodynamic minimum necessary for apatite formation, restored in vitro up to 71% of the mineral lost from caries artificially induced in extracted bovine incisor enamel. ACP cosynthesized with glass- forming fillers enhanced the mechanical properties of the resin-based composites without compromising their remineralization potential. Studies during FY99 show that ACP-filled methacrylate composites have mechanical properties that could make them suitable as cavity lining agents in restorative dentistry. When used for this purpose, their ion releasing properties may also be advantageous in reducing pulpal irritation by stimulating reparative dentin formation. - Amorphous calcium phosphate,Methacrylate resins, Dental composites, Remineralization, Enamel